The present invention relates to the bone cutting apparatus and method. More particularly, the present invention relates to an apparatus and method for forming a preliminary cut in a proximal end of a bone to guide insertion and establish the position of a prosthetic implant within the bone.
It is known to install prosthetic implants into a resected end of the bone to replace the humeral head in a total shoulder arthroplasty. The humeral implant typically includes a body portion which is inserted into the resected proximal end of the humerus. A stem is coupled to the body portion. The stem passes into the intramedullary canal of the humerus. The body portion of the humeral component typically includes a plurality of fins designed to anchor the body portion of the implant within the bone and to provide rotational stability of the implant.
It is also known to provide a series of broaches having an increasing size to cut the bone from the proximal end of the humerus to permit installation of the implant. Typically, the broaches are inserted into the resected end of the humerus and removed to remove bone. The largest broach is typically sized to be slightly smaller than the implant so that the implant can be press-fit into the canal in the bone formed by the largest broach. The broaches typically include fins corresponding to the fins on the implant.
It is also known to provide a box osteotome which cuts a rectangularly shaped section from a resected bone prior to insertion of a broach. The box osteotome does not attempt to mimic the shape of the implant.
One object of the present invention is to provide a cutting apparatus having substantially the same cross sectional size and shape as the broach and implant to cut a pattern in a proximal end of a bone for guiding insertion of the broach and implant into the bone.
Another object of the present invention is to provide a modular cutting apparatus capable of preparing the proximal end of the bone for receiving a prosthetic implant which has mismatched sizes of a body portion and to a stem.
Another object of the present invention is to provide cutting apparatus which establishes the size of the implant and controls the version of the implant.
According to one aspect of the present invention, an apparatus is provided for preparing a bone for receiving a prosthetic implant which has a body portion and a stem portion. The body portion of the implant includes a plurality of fins arranged in a predetermined pattern on the body portion. The apparatus comprises a cutter including means for cutting fin tracks in the bone to guide the plurality of fins on the implant as the implant is installed into the bone. The apparatus also includes a rod coupled to the cutter for locating the cutter relative to an intramedullary canal of the bone, and means coupled to the cutter for driving the cutter and rod into the bone.
In the illustrated embodiment, the means for cutting fin tracks in the bone includes a plurality of fins formed on the cutter and arranged in the same pattern as the plurality of fins on the body portion of the implant. The fins on the cutter cut the bone in a predetermined pattern to guide installation of the implant.
According to another aspect of the invention, an apparatus is provided for preparing a bone for receiving a prosthetic implant which includes a body portion having a predetermined size and a stem portion coupled to the body portion. The stem portion of the implant has a selected one of at least two different stem sizes. The apparatus includes a cutter for cutting the bone to prepare the bone for receiving the body portion of the implant, and at least two rods having different sizes corresponding to the at least two different stem sizes. The apparatus also includes means for coupling a selected rod having a size corresponding to the selected size of the stem to the cutter. The rod is removable from the cutter to permit a rod having a different size to be selectively coupled to the cutter depending upon the selected size of the stem of the implant. The apparatus further includes means coupled to the cutter for driving the cutter and the selected rod into the bone.
In the illustrated embodiment, the cutter has a size corresponding to the predetermined size of the body portion of the implant. The body portion of the implant includes a plurality of fins arranged in a predetermined pattern on the body portion, and the cutter includes means for cutting fin tracks in the bone to guide the plurality of fins on the implant as the implant is installed into the bone.
According to yet another aspect of the invention, an apparatus is provided for preparing a surface of a bone for receiving an implant having a body portion with a predetermined shape and a stem portion. The apparatus includes a cutter for cutting the surface of the bone in a pattern corresponding to the predetermined shape of the body portion of the implant, and a rod coupled to the cutter for locating the cutter relative to the bone. The apparatus also includes a collar slidably coupled to the cutter in a predetermined orientation. The collar is configured to engage the bone to determine a proper rotational position of the cutter relative to the bone about a longitudinal axis of the rod. The apparatus further includes means coupled to the cutter for driving the cutter and rod into the bone.
In the illustrated embodiment, the body portion of the implant includes a plurality of fins arranged in a predetermined pattern on the body portion, and the cutter includes a plurality of fins arranged in the same pattern as the plurality of fins on the body portion of the implant so that the cutter cuts the bone in a shape corresponding to the shape of the body portion of the implant. The collar is formed to include a plurality of slots for receiving the plurality of fins of the cutter therethrough to align the collar in the predetermined orientation relative to the cutter.
According to still another aspect of the invention, a method is disclose for preparing a bone for receiving a prosthetic implant which includes a body portion having a predetermined size and a stem portion coupled to the body portion. The stem portion has a selected one of at least two different stem sizes. The method includes the steps of reaming an intramedullary canal of the bone with a reamer to determine the selected size of the stem, and selecting a cutter and a rod having sizes corresponding to the sizes of the body portion and stem of the prosthetic implant, respectively, from a set of cutters and rods having various sizes. The method also includes the steps of coupling the selected cutter and the selected rod together to form a cutting apparatus, and driving the cutting apparatus into the bone so that the rod enters the reamed intramedullary canal of the bone and the cutter cuts the bone in a pattern to establish the position of the implant relative to the bone. The method further includes the step of installing the implant into the bone using the cut pattern as a guide.
The illustrated method further includes the step of rotationally aligning the cutting apparatus relative to the bone prior to the driving step. The aligning step includes the step of placing a collar on the cutter in a predetermined orientation and rotating the cutting apparatus about a longitudinal axis of the rod until the collar is substantially parallel to a resected surface of the bone.
Also in the illustrated method, the installing step includes the step of inserting and removing broaches having increasing size into the bone using the pattern cut by the cutter as a guide. The installing step also includes the step of inserting the implant into a canal cut by the broaches.
Additional objects, features, and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived.